No, you're missing the threaded stud that uses a nut to hold the wiper down on the splined taper.
If you're the tool enhanced type, you could file a flat spot, drill and tap a new internal thread in the shaft and use a bolt and washer to hold the wiper arm on. ( I have no idea how hard that splined shaft is, but it its over 35RHc, your SOL with a hand drill and tap, guaranteed one or the other or both will break)
Or if your completely stuck but have a welder, you could tap (with a hammer) the new wiper arm onto the splined shaft and tack weld the wiper arm to the face of the broken shaft. (semi permanent solution and a bit on the hoopty side)
Or you can order a reman unit for less than 100 bucks. You didn't say what year or mdl, so I chose mine.
Buy 1996-1997 Lexus LX450 Windshield Wiper Motor Front A1 Cardone for a low price of $106.97 at PartsGeek. FLAT RATE SHIPPING on most A1 Cardone 43-2001 orders.
From the package it appears it is not a rear wiper but there may be an adapter needed. My recommendation is to return it and go to Autozone where they will provide and INSTALL it for you.
Adding a somewhat random bit of info under this thread title, should anyone run into the same issue. This is a simple/crude and potentially temporary fix if the teeth on the inside of your rear wiper bolt are too worn, and the motor assembly no longer holds the bolt and thus doesn’t turn the wiper. This does not apply to the outer teeth that the wiper arm itself attaches to. I’m not sure you can just replace the toothed bolt, and if you can, the teeth holding it in place on the assembly may be too worn anyway. Typically you need to replace the whole assembly. I’m cheap and we don’t have junkyards around here, so I tried this and it worked for me. I used a 1/16 bit to drill a 1/2” or so deep hole on the side of the bolt head thingy, and then sacrificed the solid end of the bit (I have a few) as a peg to hold things in place. I first tried a wire of the same thickness, but it wasn’t stiff enough. Didn’t know if this would work, as I don’t know what’s actually inside there, but it does the job and isn’t making anything worse, considering it’s already stripped. I put a dab of blue loctite to help it stay in place, but the fit seems snug enough without. We’ll see if this lasts, but in theory should hold me over until I decide to replace the assembly in the future. Now the pesky part is that like many of us, my wiring to the rear hatch is weak/brittle after all these years of use, so I have to fiddle with it anytime I use the hatch.